1. Field of the Invention
The present invention relates to an analog-to-digital conversion apparatus. More particularly, the present invention relates to a time-interleaved analog-to-digital conversion apparatus.
2. Description of Related Art
With development of technology, demanding of electronic products is increased accordingly. Besides good qualities and powerful functions of the electronic products, low prices thereof are also important references considered by consumers during purchasing. With quick development of fabrication abilities for electronic devices, working frequencies of the electronic devices are increased accordingly. Therefore, a conventional parallel processing structure having relatively more electronic devices for matching the working frequency thereof is now replaced by a time-interleaved structure which resource are shared, so as to reduce a fabrication cost thereof.
In a digital television system, a plurality of analog-to-digital conversion (ADC) apparatuses are generally applied to capture and digitalize image signals, conventionally. Referring to FIG. 1, FIG. 1 is a block diagram illustrating a multi-channel analog-to-digital conversion apparatus 100 of a conventional television system. Since the image signals include a luminance signal and two chrominance signals, the multi-channel analog-to-digital conversion apparatus 100 accordingly includes three independent analog-to-digital converters 110, 120 and 130. Moreover, the analog-to-digital converters 110, 120 and 130 respectively receive image signals CH1˜CH3, and respectively receive gain signals GAIN1˜GAIN3 provided by gain digital-to-analog converters 140, 150 and 160 for amplifying conversion results of the analog-to-digital converters 110, 120 and 130. A clock signal Fck provides a working frequency for the analog-to-digital converters 110, 120 and 130.
Since the analog-to-digital conversion apparatus 100 applies a plurality of the analog-to-digital converters 110, 120 and 130, relatively more circuits are applied in the apparatus, and therefore cost thereof is expensive. Thus, based on the conventional technique, another analog-to-digital conversion apparatus applying a time-interleaved technique is provided.
Referring to FIG. 2, FIG. 2 is a block diagram illustrating a time-interleaved analog-to-digital conversion apparatus 200 of a conventional television system. A multiplexer 210 of the conventional time-interleaved analog-to-digital conversion apparatus 200 performs time-division multiplexing to the input image signals CH1˜CH3. Therefore, to achieve a function as that does of the analog-to-digital conversion apparatus 100, the conventional time-interleaved analog-to-digital conversion apparatus 200 requires only one analog-to-digital converter 220. However, to reduce the number of the analog-to-digital converters, the time-interleaved analog-to-digital conversion apparatus 200 has to apply a clock signal Fck3 with a relatively high frequency. In a general television system, the working frequency thereof is not high. Therefore the time-interleaved analog-to-digital conversion apparatus 200 can apply the clock signal Fck3 with the relatively high frequency.
However, the analog-to-digital conversion apparatus 200 only applies one gain digital-to-analog generator 230 to generate the amplified gain. Such amplification is to enhance intensities of the image signals, so as to enhance a signal-noise ratio (SNR) thereof. Limited by a bit number of the analog-to-digital converter 220, it is difficult for the same gain to effectively amplify three different image signals. For example, when the luminance signal is relatively great, only a relatively small gain may be applied, so that the probably small chrominance signal cannot be effectively amplified, and therefore the SNR of the chrominance signal is quite low, or even the chrominance signal may be lost.